Arlington County, Virginia, Arlington National Cemetery, Arlington, Virginia, Tomb Of The Unknown SoldierThe 100 Year Anniversity Of The “Tomb Of The Unknown Soldier” November 11, 2021November 12, 2021 Hamilton Historical Records On March 25th, 1926, the first day a permanent guard was posted, a cavalry soldier stood guard at the “Tomb of the Unknown Soldier” at the Arlington National Cemetery. (Courtesy of the Library of Congress)